For example, in a system disclosed in Patent Literature 1, a PM sensor (particulate matter sensor) is provided for detecting particulate matter (hereunder, also referred to as “PM”) in an exhaust passage of an internal combustion engine. The aforementioned PM sensor includes an insulating substrate and a pair of electrodes that are disposed on the insulating substrate with a space therebetween.
When PM contained in exhaust gas accumulates between the pair of electrodes of the PM sensor, the electrical conductivity between the electrodes changes. There is a certain correlation between the accumulated PM amount and the electrical conductivity between the electrodes, and the resistance between the electrodes changes in accordance with a PM accumulation amount between the electrodes. There is also a correlation between an accumulated PM amount between the electrodes and a PM amount contained in the exhaust gas. Accordingly, a PM amount contained in the exhaust gas is detected by detecting a resistance value between the electrodes of the PM sensor.
In the technology disclosed in Patent Literature 1, the PM sensor is disposed downstream of a diesel particulate filter (hereunder, also referred to as “DPF”). In the system disclosed in Patent Literature 1, determination of the existence or non-existence of a malfunction of the DPF and the like is executed by detecting a PM amount discharged on the downstream side of the DPF, based on the resistance value between the electrodes of the PM sensor.